The present disclosure generally relates to injection molded thermoplastic single filter media layer and multi-filter media layer filter cartridges that include a novel arrangement of structural features to improve both the quality of the manufacturing process and the integrity of the filter media layer seal and more particularly to a process for manufacturing both single filter media layer and multi-filter media layer filter cartridges and to the single filter media layer and the multi-filter media layer filter cartridges produced thereby and even more particularly to a process for manufacturing a multi-filter media layer filter cartridge without cracking the upper most filter media layer or any filter media layer during the compressing of at least two porous filter media layers between an inlet and an outlet while insuring an effective seal and the multi-filter media layer filter cartridges produced thereby and, yet, more particularly, to single filter media layer and the multi-filter media layer filter cartridges using only a single inlet design configuration and a single outlet design configuration for manufacturing a plurality of different single filter media layer filter cartridge configurations and a plurality of different multi-filter media layer filter cartridge configurations.
Molded plastic filters and multi-filter media layer filter cartridges are well known and enjoy a wide use and general acceptance in a variety of industries. As is known to those skilled in the art, the function of such units is to remove contaminants from liquid or gaseous materials, which flow therethrough. These units have proven to be particularly important in the pharmaceutical and biopharmaceutical industry where they are used to filter bacteria, leukocytes, clots, particles, gases and other contaminants from solutions before being introduced into the human blood stream, although they may have other applications including, but not limited to, high purity water or solvents. In certain critical medical applications, it is known to be imperative that the fluid not bypass the filtering media elements. When using depth media that consists of a combination of cellulose and filteraids such as described in U.S. Pat. Nos. 4,007113, 4,366,068, 4,606,824 and 4,859,340, which find particular function where sub-micronic filtration must be achieved, it is important that the seal not damage the media. Owing to its constituents, such media is prone to brittleness, especially if subjected to excessive crimping at the edge. Therefore, it is necessary to provide an undamaged, leak-proof single media layer or a multi-filter media layer filter cartridge to prevent leakage around the filter media layer(s) contained therein.
Typically, smaller filter devices used to filter bioprocess or pharmaceutical solutions are made up of two-part housing with an internally disposed filter media layers sandwiched between the two housing members. Typically, the manufacturing process for thermoplastic filter units entails first the injection molding of the two housing members. Once the housing members have been molded, the filter media layers are usually placed on the outlet-housing member over the outlet opening. The inlet housing element is then positioned over the outlet-housing member sandwiching the filter media layers between the two housing members. In some known prior art devices, the edges of the filter media layers remain exposed at the joint between the housing members. The inlet housing member, outlet housing member and filter media layers are then sealed together by any of a variety of methods including, pressure clamping, heat sealing, ultrasonic welding, or the use of a thermoplastic overmold band, as is known to those skilled in the art. In particular, the use of an overmold band offers the advantage of adding significant structural strength to the multi-filter media layer filter cartridge.
There are a number of prior art patents that have been directed to solving problems in this general area. There are two U.S. patents that generally describe the process of sealing a filter with a thermoplastic overmold band, U.S. Pat. No. 4,113,627, to Leason issued on Sep. 12, 1978 which, describes a process for the injection molding of a thermoplastic overmold band over two thermoplastic housing members having an exposed filter element sandwiched there between and U.S. Pat. No. 4,414,172, to Leason issued on Nov. 8, 1983 which, describes a process for the injection molding of a thermoplastic overmold band over one housing member and an exposed filter element, the disclosure of each is herein incorporated by reference to the extent not inconsistent with the present disclosure.
Several more recent prior art patents include U.S. Pat. No. 5,556,641, to Ruschke entitled Process of Making Hermetically Sealed Filter Units and Filters Made Thereby, issued Sep. 17, 1996 and the divisional U.S. Pat. No. 5,688,460, to Ruschke, entitled Process of Making Hermetically Sealed Filter Units, issued Nov. 18, 1997 which related to a process for the manufacture of intravenous solution filter units includes injection molding a sealing member onto the periphery of the assembled filter components to hermetically seal the components into an integral assembly, the disclosure of each is herein incorporated by reference to the extent not inconsistent with the present disclosure. The filter unit itself includes a housing and a filter element disposed internally thereof. The filter element is supported by a grid having a design and placement within the housing to assure, in conjunction with other structural features of the filter, the complete purging of gases from the filtrate. Also disclosed was a method for hermetically sealing the filter element to its thermoplastic support, which provides an improved seal, which will not leak. The disclosed method comprises the molding of the support, the alignment of the filter element on the support, the application of pressure to hold the element on the support and the overmolding of the periphery of the element to seal the edge of the element to the support.
U.S. Pat. No. 5,798,041, to Zuk, Jr. entitled In-Line Liquid Filtration Device Usable For Blood, Blood Products Or The Like, issued Aug. 25, 1998, which relates to an in-line liquid filtration device useable for filtration of blood, blood products or the like includes a housing having an inlet port, an outlet port, at least one filter element disposed in the housing between the inlet port and outlet port so as to filter liquid which flows into the filtration device via the inlet port, the disclosure of which is herein incorporated by reference to the extent not inconsistent with the present disclosure. The filter element divides the housing into a first chamber and a second chamber. The device allows gases to vent the filtration device through the outlet port. The means may include a flow deflector within the first chamber and/or the second chamber. The means may also include a channel, preferably spiral, within either the first chamber and/or second chamber. The filtration device allows air therein to be purged downstream either into an air-collecting bag or into the blood-receiving bag without the manipulation of the height of the filtration device or the blood-receiving bag.
The seal rings in the existing patent were designed in a stepped fashion and were mounted outside of the filter media. The distance from the internal “stepped” surface to the overall height determined the amount that the filter media would be compressed. In order to achieve a leak proof seal in all of the varying applications, several different seal rings needed to be designed and incorporated due to the several different thicknesses, densities and compression requirements of the filter media.
The seal rings needed to be press fit or otherwise bonded to the outlet in one way or another in order to create a leak proof seal and prevent bypass of fluids from the upstream to the downstream sides. In the existing design, the compression of the filter media and the overmold material form a leak proof seal and prevent bypass of the filtrate.
The above are but a few examples of a multitude of representative prior art patents that are directed to the general subject matter of the present disclosure.
In contrast to Zuk, Jr., the seal described in the present disclosure is not stepped, and is placed within the outside diameter (OD) of the filter media layers. The seal design and placement allows the filter media to be compressed however much is required in order to create a molding seal during the forming of the exterior overmold. As will be described in detail below, compressive forces from the mold cavity and core plates are transferred through the inlet, the outlet, the seal(s) and each piece of filter media, with the amount of compression being adjustable within the mold.
Our initial concept, as illustrated in FIG. 1, was a multi-filter media layer filter cartridge having multiple filter media layers and no seal rings positioned between the multiple filter media layers. However, when tested, this concept usually resulted in unwanted cracking of the upper filter media layer(s) 23. In the multi-filter media layer filter cartridge 20 illustrated, the filter media layers are stacked between an inlet 24 and an outlet 26. All components are then loaded into a mold, compressed between a cavity and core and overmolded with plastic 28 to seal the filter media layers therein. The multi-filter media layer filter cartridge is designed such that when it is compressed between the cavity and core, the filter media layer(s) deform at the perimeter 30 thereof. This compression is done to collapse and close all of the pores of the filter media layer(s) in order to prevent resin from passing through the filter media layers and into the center 32 of the multi-filter media layer filter cartridge. To compensate for varying filter media thicknesses and stack heights, the mold is adjustable to create varying amounts of compression.
FIG. 1 also illustrates the two problems that the seal ring(s) 34 (see FIG. 4) of the present disclosure are designed to resolve. First, as mentioned above, when compressed, two or more stacked filter media layers 22 often crack 36. In the assembly of the multi-filter media layer filter cartridge 20, the first filter media layer 21 is laid flat against the outlet 26. The second 22 and third filter media layers 23 are then laid on top of the first 21. Finally, the inlet 24 is laid on top of the upper most filter media layer 23. During the compression stage of the overmolding process, the bottom filter media layer 21 deforms due to compression at the perimeter 30 thereof. The middle filter media layer 22 deforms due to compression and due to bending caused by the compression. As the multi-filter media layer filter cartridge 20 is compressed in the mold, the middle filter media layer 22 has to first follow the contour of the bottom filter media layer 21 and also has its perimeter 30 compressed. As compression continues, the top filter media layer 23 then is deformed even more than the middle filter media layer 22 as it bends over the increased height of the contour of the middle filter media layer 22 as the perimeter 30 of the top filter media layer 23 is compressed. The stress on each filter media layer increases as the number of filter media layers increases. As a result, the top filter media layer 23 has been found to easily crack 36 and thus, to provide a path for the filtrate to follow without having to pass through the filter media layer pores. Such cracking has been found to not be limited to the uppermost filter media layer 23, as the middle filter media layer 22 and other intermediate filter media layer(s) have also been found to crack and thus reduce the cracked filter media layers effectiveness as well.
Second, it was also determined that in order to support the sealing surface and create a chamber to allow fluid to enter between the top most media layer and the inlet, and reduce hold up volume, different configurations of the inlet part were required to manufacture the embodiment of FIG. 1. Specifically, if only one filter media layer were to be included in the assembly, a relatively short walled inlet configuration would be preferred to reduce hold up volume, as illustrated in FIG. 2. On the other hand, if two or more filter media layers were to be used in the multi-filter media layer filter cartridge assembly a relatively taller walled inlet configuration would be required, as illustrated in FIG. 1. While it may be possible to use a taller walled inlet to make a filter cartridge with a single media layer, this would create un-wanted extra hold up volume, which is undesirable.
However, now it has been determinate that a single inlet design configuration can be utilized with one, two, three or more filter media layers thereby eliminating the need for two or more different inlet design configurations, which results in a significant simplification of the manufacturing process. This was achieved because one filter media layer units required that the inlet have a specific headspace in order to accommodate fluid flow. If an additional filter media layer was added to the first filter media layer, the compression forced both layers further into the head space requiring more head space to sufficiently accommodate fluid flow. However, the spacer element eliminates the need for this additional headroom to be built into the part because it adds the volume only as it is needed. The seal ring is simpler to mold than multiple inlets.
Therefore, a need exists for a manufacturing method, which will eliminate the problem of filter media cracking found in some prior, art methods of manufacturing multi-filter media layer filter cartridges and reduces the number of constituent parts thereby simplifying the manufacturing process for a single filter media layer and multi-filter media layer filter cartridges and the single layer filter media and the multi-filter media layer filter cartridges produced thereby.